The general operation of thermal inkjet imaging devices is well known and one description of such operation may be found for instance in U.S. Pat. Nos. 6,464,316 and 6,536,869, which are incorporated in their entirety by reference herein. An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations may be visualized as dots in a rectilinear array or pixels. Thus, a printing operation may be viewed as filling a pattern of pixels with dots of ink.
Inkjet imaging devices print dots by ejecting small drops of ink onto a print medium. Typically a movable carriage supports one or more printheads each including ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at selected times controlled by a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of an image being printed.
A typical inkjet includes an array of nozzles attached to a printhead that includes an array of chambers for receiving ink from a reservoir. Each chamber is fluidly connected to a nozzle so ink can collect in the chamber and the nozzle. A firing resistor is associated with each chamber. Ejection of an ink drop is typically controlled by a microprocessor, the signals of which are conveyed by electrical traces to the firing resistors. When electric printing pulses heat the resistor, a portion of the ink vaporizes and a drop of ink is ejected from the nozzle. Nozzles are commonly arranged to form a dot matrix pattern. The controlled firing of each nozzle causes characters or images to be printed upon a media as the printhead moves past the media.
In inkjet printing, data representative of an image is composed of a set of data comprising a two dimensional array based on x and y coordinates of “pixels”. Pixel location is specified by its x and y coordinates in the array. The x coordinate of the pixel may be referred to as the row coordinate value, and the y location of the pixel may be referred to as the column coordinate value. The term “image data” is used herein to refer to an array of pixels having digital code values that form an image.
Specific inking patterns used in each pass, and the manner in which the inking patterns cumulatively form an image, is known as a printmode. Manipulation of printmodes allow the printer to control various factors that influence image quality, including the amount of ink placed on the print media at any given pixel, (image density), the speed with which the ink is placed, and the number of passes required to complete the image. A printmask is a binary pattern that defines which ink drops are printed in a given pass, which passes are used to print any given pixel and which nozzle will be used to print any given pixel location. Thus, the printmask defines both the pass and the nozzle which will be used to print each pixel location, i.e., each row number and column number on the media. A printmode typically defines one or more printmasks used in printing an image, the number of passes required to complete any given portion of the image and the number of drops per pixel.
The printhead is scanned repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of movement across the medium, each nozzle may or may not be print enabled or signaled to fire, according to an output of the controlling microprocessor. Each completed movement across the medium can print a pass approximately as high as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed print pass the medium may be advanced by a media feed mechanism a distance substantially equal to a height of the pass or a fraction thereof. The carriage reverses direction and the ink cartridge begins the controlled deposition of ink drops for a subsequent pass.
Under various environmental conditions and with duplex printing, media sometimes curls causing edges of media to lift off a platen surface where printing occurs. This may be a problem with scanning inkjet printheads because print quality is best when printheads are positioned close to media. If edges lift up, the printheads will catch on them and damage media, printheads and/or the printer as the printheads scan across the media. If the media edges are held down though the entire print-zone length, large print margins will be required.
Previous solutions have included holding the media down for the entire printzone length, observing a narrower printzone. This solution, however, does not allow for small margin or full bleed printing. Another solution has been to hold the media edges down just upstream of the printzone. Another solution has been to angle the media down at the platen where printing occurs and not support the media at the edges so the media continues to angle down away from the printheads as it progresses further into the printzone. Both of these solutions provide acceptable results for shorter printheads and printzones but become increasingly less efficient with the increase in size of printheads and printzones. Vacuum systems may also be employed to hold down media edges but these systems are expensive and vacuum levels may affect ink drop trajectory and linefeed advance accuracy.
It may, therefore, be advantageous to provide media guides in the printzone that engage the edges of the media and guide the media in through at least a portion of the printzone. Nevertheless, placement of edge guides within a printzone, even if such edge guides only obstruct a marginal portion of the print media pose a challenge to structuring print routines that are capable of either printing within or around such obstructions.
Advantage may also be found in providing a print routine operable by an inkjet imaging device that allows for small margin and/or full bleed printing in an area of the printzone that is defined as a print disable zone or that includes an obstruction between the print media and the printhead.